The present invention relates to an automatic sampling apparatus for the injection of samples to be analyzed in a gas chromatographic column, and more particularly, to such an apparatus designed to be used in case of sample injections by means of non-vaporizing direct on-column injectors. The present invention further relates to a switch valve designed for such apparatus, as well as to a sampling method to be used with such apparatus and switch valve.
Among the equipment available to perform chemical analysis of liquid samples by gas chromatography, there are known automatic samplers which allow the feeding of a series of samples to be analyzed to an injector connected to the head of a gas chromatographic column. These automatic samplers are, for example, constructed in a manner which requires removal of the injection syringe from the sample vial and its insertion into the injector. However, these known automatic samplers possess many drawbacks. To this end, it is preferred to employ automatic samplers of the type where the injection syringe remains fixedly aligned with the injector.
These last mentioned automatic samplers generally include an automatic device which is capable of drawing the sample to be analyzed from a container, e.g., a vial, and of feeding it to an injection syringe mounted in alignment with the inlet part e.g., injection port, of an injector. Automatic means are provided which are capable of washing the whole sample feeding system in such a way that, at the end of the injection stage of each sample, the device is ready for feeding the syringe with a new sample, without the danger that the syringe is contaminated by traces of the previously injected sample. In addition, automatic means are provided which actuate the movement of the injection syringe needle into and out of the injector. Further, automatic means are provided for measuring the exact amount of sample to be introduced into the gas chromatographic column and automatic means are provided for introducing the sample into the gas chromatographic column. In order to drain the washing liquid and the excess sample coming out from the injection syringe, thus preventing them from penetrating the injector body and contaminating it, a switch valve is generally provided between the injection syringe and the injector.
The aforementioned known equipment, however, cannot be used with on-column type injectors. In particular, the first type does not provide perfect alignment between the syringe needle and the on-column injector, while the second type, as the first type, requires the use of sample injection syringes equipped with very thin needles which are capable of penetrating inside the gas chromatographic capillary column having an internal diameter of approximately 0.2-0.3 mm. The peculiarities of on-column injectors represents a considerable problem. That is, the aforementioned switch valve is generally constructed to include a rubber septa generally not pierceable by extremely thin needles, such as those used in on-column injectors. Moreover, the automatic means actuating the injection syringe needle movements into and out of the injector do not assure a sufficient precision of operation, as necessary for a safe introduction into the gas chromatographic column of the very thin and extremely flexible needle used with the on-column type injectors.